The present invention is generally related to treating ballast water and, more particularly, is related to an apparatus and method of treating ballast water contaminated with organisms with a biocide.
Every year the United States receives an estimated 80 million tons of ballast water. The ballast water comes from the practice in the shipping industry of ships pumping water into the ballast tanks system to balance the ship in the water. The ship requires balancing because the load (e.g. cargo) on the ship may not be equally dispersed throughout the ship. Once the ship is balanced, it travels to a new port and pumps out the ballast water, as required, to balance the ship after loading/unloading. In other words, ships necessarily transfer ballast water from one port and then discharge that ballast water at another port. In addition, the ballast water can come from ocean going vessels such as self unloading carriers, RO/RO carriers, ferries, and tug/barge combinations. Ballast water discharge has been known to contaminate coastal ecosystems and harbors. The contamination results from the ballast water carrying aquatic organisms and micro organisms such as pathogens, microbial species and more specifically V. cholera, E. Coli, Salmonella species, Crystosporidium species, Hepatitis A virus, enterovirus, etc.
In 1996, Congress passed the National Invasive Species Act (P. L. 104-332) to stem the spread of non-indigenous organisms by ballast water discharge. The Act requires the Secretary of Transportation to develop national guidelines to prevent the spread of organisms and their introduction into U.S. waters via ballast water of commercial vessels. The Act establishes guidelines that require that vessels that enter U.S. waters after operating undertake ballast exchange in the high seas. In this method, a vessel empties its ballast on the high seas and refills the ballast tanks with sea water. However, the emptying of ballast tanks causes an imbalance that makes the exchange of ballast water exchange on the high seas both dangerous and sometimes impossible because of weather conditions. Additionally, high seas exchange requires manpower that many vessels do not have or cannot economically provide.
Many attempts to develop suitable methods for treating ballast water of ships have been proposed, but all of these are ineffective in treating the wide variety of organisms found in ballast water. Additionally, many proposed biocides are harmful to the environment due to toxic by-products, and/or have high operation costs. In particular, ultra violet radiation techniques have been used in trials, but this technique is not effective for many organisms and has been found to be ineffective in turbid water. In addition to ultraviolet irradiation, ozonation has been used in trials as a biocide, but ozonation of ballast water is complex and very expensive. Other chemicals, such as hypochlorite, have been used as a biocide, but hypochlorite forms dangerous organochlorine compounds and is corrosive to the ballast tanks of the vessel.
An additional problem for many of the other biocides is the formation of the bromate ion as a by-product. Many biocides, such as ozone, hypobromous acid, and hydrogen peroxide, produce bromate ions due to their high oxidative reduction potential. The bromate ion is known to be a carcinogenic to humans and is very toxic to marine animals. This poses a problem for the bodies of water receiving ballast water treated with these chemical.
A further problem with other biocides is that they are not effective in treating biofilms. This is important because biofilms may have 500-500,000 bacterium attached to its surface for every bacterium found in bulk ballast water. In this regard, biofilms contain many target organisms and, therefore, need to be treated to kill the target organisms living in the biofilm.
Thus, a heretofore unaddressed need exists in the industry to address the problem associated with treatment and discharge of ballast water.
Briefly described, the present invention provides a ballast water treatment system. The ballast water treatment system includes a control system and a ballast tank system. The control system controls the concentration of a biocide in the ballast tank system.
In addition, the present invention provides a vessel that includes a control system, a biocide generation system, and a ballast tank system. The control system is capable of controlling the concentration of a biocide in the ballast tank system by controlling the amount of the biocide feed into the ballast tank system from the biocide generation system.
The present invention also involves methods for controlling organisms in ballast water of a vessel. A representative method includes providing the ballast water, and treating the ballast water with chlorine dioxide.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.